Mr heater big maxx size and venting?

[ride92]

i think I’m going to go with a Mr Heater Big maxx garage heater for 1140sqft attached garage in Wisconsin. Would you guys recommend the 50k or 80k btu for that size? I’ll be insulating the walls with R15 and do at least R38 in the ceiling.
I’ll be doing vertical venting, how far away from adjacent exterior walls do I need to be. I know with reznor and modine it spells it out pretty clearly that I have to stay at least 6ft from a vertical wall for the outside vent is that same for the mr heaters?

and lastly, it seems quite a few people go with just the regular garage heater over the separated combustion ones. I do your basic garage stuff, small engine stuff, car and motorcycle stuff, detailing, small wood projects. Are these generally safe to use or should really be spreading 3x the price for a separated combustion unit?

 

[PoorUB]

50K will be more than enough, do not go with the 80K as it will be too large and short cycle and rot out the heat exchanger.

You should be able to go to the manufacturer's web site and download a installation manual and get correct information.

 

[Jakemedic]

The owners manual spells it out quite clearly. I opted for horizontal venting when I put mine in. For some reason I could not get myself to cut a hole in a brand new metal roof. Have fun with your project! I went with a 50k and it would adequately heat your space.

 

[The Cobbler]

X3 on the dimensions required
money on sealed comustion? I wouldn't worry for what you propose you do.

 

[toyotadriver]

I have an 80k for a 1200 sq ft with 10ft ceilings. Similar insulation. Warmer climate though. 2 9 ft garage doors, 1 walk through door, and 2 windows. I had a 45k and it would heat it but it didn’t heat it up as quickly as I wanted. I only heat it when it’s being used. In the coldest months, it stays around 40* or so inside and when I use it, I heat it to 62-68* depending on what I’m doing. I wanted a faster temp rise so I upgraded to the 80k. I don’t regret my decision at all.

In your case, if you heat it all the time and just bump it up when you are out there, I’d go with the 50k. If you are like me and only heat it when you work out there, you’ll definitely want the extra BTUs and you should go with the 80k.
Some people want to size garage heaters like you size a house heater. Well, you really can’t. If you have garage doors even well insulated doors lose heat more than house walls so you need more BTUs. You heat your house all the time but most people don’t heat their garage or shop all the time so you need more BTUs if you only heat it when you work there.


I do similar work in my shop and don’t have a sealed combustion heater and haven’t needed it.

 

[finn]

50 k will be adequate. Try to warm it up once or twice per week to keep the slab warm. The slab is a huge heat sink, and keeping it warm improves the comfort level.

You’re not painting cars or running a commercial wood shop so there’s no need for separate combustion.

 

[Showkey]

Agree on the 45-50k ………1000 sqft well insulated in central Wisconsin. The or owner had installed @ 75k unit it worked well for me …….don’t know his habits or use ………but that unit failed and was very rusty. I replaced it with 50k unit it been all good. Mine is CAT III horizontal vent.

As a side note the original install was a pro install with B vent horizontal. It was very rusty when I moved in aftrer 17 years of unknown use. I replaced with B vent. That new B vent also rusted more than one would expect, few years later replaced the unit and used CAT III. All good …….

Theres no long term savings with B vent……..horizontal vent and CAT III has real merit in most situations.

 

[TractorJeff]

Southeastern Wi! I keep mine around 45/50, bumping up to 62 when I am out there. Work on all kinds of projects/equipment. Have had good success with a Big Max 50k on a horizontal Vent. Couldn't bare the thought of cutting a hole in a metal roof! I believe the Manual states a minimum of 6 inches from the ceiling(?). Can't remember?? Only regret I have is not insulating around the Slab as the snow melts away.

 

[ride92]

I have an 80k for a 1200 sq ft with 10ft ceilings. Similar insulation. Warmer climate though. 2 9 ft garage doors, 1 walk through door, and 2 windows. I had a 45k and it would heat it but it didn’t heat it up as quickly as I wanted. I only heat it when it’s being used. In the coldest months, it stays around 40* or so inside and when I use it, I heat it to 62-68* depending on what I’m doing. I wanted a faster temp rise so I upgraded to the 80k. I don’t regret my decision at all.

In your case, if you heat it all the time and just bump it up when you are out there, I’d go with the 50k. If you are like me and only heat it when you work out there, you’ll definitely want the extra BTUs and you should go with the 80k.
Some people want to size garage heaters like you size a house heater. Well, you really can’t. If you have garage doors even well insulated doors lose heat more than house walls so you need more BTUs. You heat your house all the time but most people don’t heat their garage or shop all the time so you need more BTUs if you only heat it when you work there.


I do similar work in my shop and don’t have a sealed combustion heater and haven’t needed it.

I think your selling me on the 80K btu unit. Sounds like just what I want to do. How long does the 80k take to heat it up vs the 45k you had? I’m worried if short cycling but I also don’t want to wait forever for it to get warm

 

[toyotadriver]

When I'm going to work in the shop, I usually go out there and turn the heat on and then go back inside. If it's 45* inside and maybe 25* outside when I turn on the heater, it'll probably run for about 30 mins to get up to temp. (I'm guessing because I have never actually timed it). It'll usually run for 10 mins or so per run time, maybe a little more after that. Definitely longer if it's colder outside. When I had the 45k in the shop it took over 1 hr to raise the temps to make it comfortable to work. I wanted it to come up to temp faster.

A 60k would have been ideal but they don't make a 60k so I installed the 80k.

 

[D45]

When I'm going to work in the shop, I usually go out there and turn the heat on and then go back inside. If it's 45* inside and maybe 25* outside when I turn on the heater, it'll probably run for about 30 mins to get up to temp. (I'm guessing because I have never actually timed it). It'll usually run for 10 mins or so per run time, maybe a little more after that. Definitely longer if it's colder outside. When I had the 45k in the shop it took over 1 hr to raise the temps to make it comfortable to work. I wanted it to come up to temp faster.

A 60k would have been ideal but they don't make a 60k so I installed the 80k.

Kinda what I did.............I installed a 45k Hot Dawg for my shop. It worked, but took too long to heat up the space and was running alot

I sold it and bought an 75k Hot Dawg.............works much better for me and my needs. Heats up fast and doesn't run as much

My shop is also 60ish feet long, and the 45k used a small 10" fan (27' heat throw)

My 75k uses a 14" fan and heat throw is much farther (38')


Here is my install link:

Hot Dawg 45K Heater Install

Hot Dawg 45K (NOW 75K) Heater Install I picked up this used Hot Dawg 45,000 BTU natural gas heater Obviously, I need three things: -"low temp" thermostat -Duct-work, vertical roof vented I assume -Hanging kit/Mounting kit for the heater Can I put a 110 outlet plug on the wiring or...

www.garagejournal.com

 

[D45]

I personally would not spend the extra money for a sealed combustion setup

My vertical Duravent #0370 (3") kit was like $65 shipped and I did the install myself, zero leaks

 

[Showkey]

Either way the shop will be heated. So there is no right or wrong answer.
But: I don’t think anyone would say increasing your home furnace size by 66% would be

The math says 45k to 75k is a 66% increase.
Percent difference is 50% as its a different calculation.
They are both the same efficiency so to heat a space one has to run more.
So………yes 45 K would have to run a lot more.
The question is…….does a 75k unit over the entire season run for very short periods ( aka short cycling) when the outside temps are moderate ?

 

[toyotadriver]

OP...I think you'll be happier with the larger heater.

Looks like Modine Hot Dog heaters can be purchased in 60k sizes so that might be something you look into. They are more expensive than Mr. Heater furnaces though.

 

[ride92]

I ended up getting the 80K btu big maxx on sale at northern tool. Excited to get in hooked up and installed but man are the direction clear as mud with this stuff. I have lots of question on how to do all this. I’m capable of doing the work but I need to learn what it is first. Like the fire block bracket for vertical venting, does that go in up into the attic space or down from the attic space? And what do I all need inline with gas line, a shut of valve and a drain drop?

 

[D45]

Yes.....shut off off before the flexible appliance line and drip leg at the appliance

 

[toyotadriver]

Look forward to hearing what you think of it. Before I had a garage or a shop, I worked outside. It sucked but I sucked it up. I then got a small garage and I got by with unvented heaters for years. Thought it was awesome to have no cold air blowing down my neck and heat. Then, I started noticing the humidity from the unvented heater. Once I went with vented heaters in my well insulated garage and shop, I just can't go back. It's so awesome to work in comfort.

 

[PoorUB]

I would have gone with 50k, but what do I know! Pray the heat exchanger doesn't rust away in 3-4 years with that 80k!

 

[toyotadriver]

It’ll be fine. I’ve got 7 years so far using my 80k in my 1200 sq ft well insulated shop in a warmer climate than the OP. No rust. No corrosion. Just nice warm and dry heat.

 

[ShopNotShed]

Couple months late here, but I'm in Western Wisconsin and maybe jumped the gun on a 125KBTU unit from Big Maxx. I have a 30x40 with 10ft ceilings and R15 in the walls and idk what's in the ceiling but probably more. 2 9x10 OHD's, a service door that is terrible and has at least 3 inch gap on the bottom (replacing this weekend) and 6 garbage windows.

It's great. This is my first year having it and we haven't had the cold days yet but I sure like it. Hoping the heat exchanger concerns above don't happen, though.

I use a Nest Thermostat and keep it at 40* when I'm not in there and bump it to 50-60 depending on what we're doing.

I installed mine in the last few months so if you haven't done yours yet and have any questions on how I ended up doing it, hit me up. I did pretty much everything myself (and help of a couple of friends). Propane company wouldn't drop a tank and ended up doing a 125' run from my house tank to the shop, still not happy about that.

 

[gmcgeo]

Couple months late here, but I'm in Western Wisconsin and maybe jumped the gun on a 125KBTU unit from Big Maxx. I have a 30x40 with 10ft ceilings and R15 in the walls and idk what's in the ceiling but probably more. 2 9x10 OHD's, a service door that is terrible and has at least 3 inch gap on the bottom (replacing this weekend) and 6 garbage windows.

It's great. This is my first year having it and we haven't had the cold days yet but I sure like it. Hoping the heat exchanger concerns above don't happen, though.

I use a Nest Thermostat and keep it at 40* when I'm not in there and bump it to 50-60 depending on what we're doing.

I installed mine in the last few months so if you haven't done yours yet and have any questions on how I ended up doing it, hit me up. I did pretty much everything myself (and help of a couple of friends). Propane company wouldn't drop a tank and ended up doing a 125' run from my house tank to the shop, still not happy about that.

Why wont a propane company set a tank for you.

 

[ShopNotShed]

Why wont a propane company set a tank for you.

Apparently they have too many people around here with "small" shop/garage tanks that they have to fill 5+ times a year versus the house tank once a year. I even asked if they'd just drop a 500 then and no luck.

 

[gmcgeo]

Bad business on them. I would not be passing up a customer. So many option to give you a tank and if there are more ppl in your area that have tanks, that means they are in your area anyway!

 

[PoorUB]

Apparently they have too many people around here with "small" shop/garage tanks that they have to fill 5+ times a year versus the house tank once a year. I even asked if they'd just drop a 500 then and no luck.

Lots of times they consider the usage. Many people heat the shop only when they use it so the gas company drops off a 500 gallon tank and it takes the homeowner five years to use it up.
Plus, if you have one on your property already they don't want to add a second.

 

[gmcgeo]

Lots of times they consider the usage. Many people heat the shop only when they use it so the gas company drops off a 500 gallon tank and it takes the homeowner five years to use it up.
Plus, if you have one on your property already they don't want to add a second.

so my company would not set a 500 gallon for that, 1 is the price of steal is way up. so investment return would take years to set that big of a tank.

however being upfront with the customer. I tell them, if i set a 100 gallon tank and top off every other time i fill the house it pays for us to top it off. already has a tank at the house this is an easy one. charge a fee to top off?

however i don't know the real issue this company docent want to set it, has to be more then " we have more in your area that have little tanks or low use" I think there is more to the story....... maybe they are limiting the tanks being placed with the steal issues. my tanks are 10 months back ordered

 

[buddha2364]

You need to account for ceiling height here as well. I run the 80k BTU in my 1200 foot square shop and it's just adequate enough.

Fully insulated, but I have scissor trusses, giving me a peak height around 16'. All the heat goes up which was anticpated, so I run dual 50" fans as well. I don't run 24x7, but to get it from say 40 degrees to 65 degress takes about an hour and then it runs pretty often after that to maintain. The problem with not running all the time is you spend a lot of heat fighting to get objects in the shop warmed up.........the floor, vehicles, etc.

I put mine in the opposite corner of my man door, blowing diagonally across the shop. I vented out the side of the wall, it was a pretty short run, bascially right at the minimum of like 3 or 4 feet.

 

[Plump]

Great thread with some pertinent information as I try YET AGAIN to get my heater set up. Hip surgery this fall put me out of action and my procrastination in summer when the attic is 105° has put me behind!

 

[TractorJeff]

Milton Propane dropped a 125 gallon for me 2 Falls ago.
Come out at 330 gallons total for the 1st Winter for less than a 1000sqft.
The average fill is about 80 gallons!

 

[ShopNotShed]

so my company would not set a 500 gallon for that, 1 is the price of steal is way up. so investment return would take years to set that big of a tank.

however being upfront with the customer. I tell them, if i set a 100 gallon tank and top off every other time i fill the house it pays for us to top it off. already has a tank at the house this is an easy one. charge a fee to top off?

however i don't know the real issue this company docent want to set it, has to be more then " we have more in your area that have little tanks or low use" I think there is more to the story....... maybe they are limiting the tanks being placed with the steal issues. my tanks are 10 months back ordered

Yeah I think you're right about the tanks too. I wanted them to drop a 250-300 gallon tank because I knew I'd go through too much for a 100 gallon tank. Also there are not many propane providers where I am. Maybe 3.

OH well, it's done and it works. Let's just hope the trench they dug up settles nicely (hasn't since winter is here).

Also going through WAY more propane than I did last year without the shop heater, and it's pretty pricy here now.

 

[dave*99]

If you have a high ceiling you will absolutely want a ceiling fan to blow the warm air down. My old garage had a 10' ceiling and difference in air temp was huge when I climbed up a few feet on a ladder. Ceiling fan to the rescue.

 

[SlotlessMan]

I have an 80K in my well insulated 1200' w/ 10' walls. It is overkill and wish I had settled for the 50K. I keep it at 50 degrees during the winter and it used to cycle quite a bit when really cold out.

I bought a thermostat that limits the cycle to twice an hour for when I am not out there. It helped quite a bit but it will drop to the high 40s on really cold days. Not out there so not a big deal to me

 

[Plump]

If you have a high ceiling you will absolutely want a ceiling fan to blow the warm air down. My old garage had a 10' ceiling and difference in air temp was huge when I climbed up a few feet on a ladder. Ceiling fan to the rescue.

Even if you DON'T have a high ceiling, get a cheap ceiling fan to move air around. Makes a huge difference. Can dry up melted snow, get those corner areas warm, move odors, and just generally make the garage a better place.

 

[Dagny]

check where those heaters are made.